Golf club

ABSTRACT

A golf club enables a golf ball to be hit farther without a decrease in ball traveling distance even if it is struck at a lower point on the club head face. A driver club head includes a face having a hitting surface, a sole forming the bottom of the head, etc. The sole is modified for improvement by providing an elastically deformable area having a recessed or projected configuration at a position of the sole closer to the face. The deformable area includes a bent portion formed at the lower end of the face. A bend is formed between the bent portion and the sole at an obtuse angle. The sole is provided with a recess or a projection to lower the rigidity of the sole. Thus, repulsion is enhanced to increase the ball traveling distance even if the ball is struck at a lower point on the face.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to golf clubs. More particularly,the present invention relates to an improved golf club having a clubhead sole modified to increase the traveling distance of golf balls.

[0003] 2. Description of the Related Art

[0004] There are various golf clubs prepared for varying conditions ofgolf courses. For the first shot, golf clubs called “drivers” areusually used in order to get maximum ball traveling distance. The balltraveling distance affects the score directly. Therefore, the positionof the ball impact point on the golf club head is an important factor.The hitting surface of the club head is called “face”. Under anyconditions, the user (player) will strike the ball on the face of theclub head.

[0005] Usually, the center of gravity of a driver club head as projectedon the club face is located above the center of the face as seen from adirection perpendicular to the face surface. The reason for this is asfollows. The club head has an approximately inverted trapezoidal ortriangular configuration in terms of the face configuration, in whichthe upper side is wider than the lower side. Accordingly, the mass isinevitably deviated toward the upper side. In addition, because a partknown as “hosel”, into which a shaft is to be inserted, is provided onthe top of the club head, an extra mass is added to the upper side ofthe head.

[0006] Regarding the center of gravity, even a club head in which thecenter of gravity is located at a position approximately 60% from thebottom surface of the head in terms of the face height, for example, iscalled “low-center of gravity model”. A ball striking area called “sweetarea” is in the vicinity of the center of gravity, which is an areacapable of sending the ball the farthest distance. Therefore, in orderto make use of the maximum repulsion power of the head to maximize theball traveling distance, it is usually necessary to strike the ball on asweet area above the center of the face. However, not only amateurgolfers whose ball impact point is likely to vary but also professionalgolfers occasionally shift their ball impact point intentionallyaccording to golf course conditions.

[0007] For example, in a head (against) wind, golfers usually hit theball in such a manner as to produce a low ball trajectory because if itis hit in the usual manner, the ball will have to fly against the wind,resulting in a failure to get the desired ball traveling distance. Inthis case, the ball impact point is in a lower area of the club face.This, however, results in degradation of the repulsive force obtained.Consequently, the ball traveling distance achievable becomes less thanthat obtained by striking on the sweet area. This is because the centerof gravity is located at the upper side of the face, as stated above.That is, because the sweet area, which is a high-repulsion area, is inthe vicinity of the center of gravity, if the impact point is off thisarea, repulsive force reduces undesirably.

[0008] Under these circumstances, various methods have been proposed toenable a repulsive force comparable to that obtained at the conventionalsweet area to be obtained even at a lower point on the face to therebysolve the problems associated with the conventional golf clubs. Forexample, a golf club has been disclosed in which the area of a region ofthe club face that has a specific coefficient of restitution isspecified to minimize the decrease in ball traveling distance when theball impact point is offset from the sweet spot, as a method ofincreasing repulsive force [for example, see Japanese Patent ApplicationUnexamined Publication (KOKAI) No. 2002-17912]. As a method of loweringthe center of gravity and consequently increasing repulsive force at alower point on the club face, a technique has been disclosed wherein aweight member that is wider at the lower side than the upper sidethereof is provided in a lower portion of the club head [for example,see Japanese Patent Application Unexamined Publication (KOKAI) No.2002-17908]. Further, there is known a golf club having a head arrangedto allow its face to be deflected with good balance [for example, seeJapanese Patent Application Unexamined Publication (KOKAI) No. Hei11-114102].

[0009] As has been stated above, various methods have been devised toincrease the ball traveling distance under various conditions. However,the proposed methods have not yet satisfactorily solved the problems.There is still room for further improvement, particularly in terms ofenhancement of repulsion at a lower point off the sweet area. Theabove-described method wherein the area of a region of the club facethat has a specific coefficient of restitution is specified isspecifically carried out by reducing the thickness of a specific regionof the face so that the thickness varies from the center to theperipheral edge of the face, thereby consequently enhancing therepulsion effect.

[0010] The above-described face structure may be effective for specificclub heads but is not always reliable. The structure in which the clubface, including the crown, is deflectable with good balance is alsoincapable of surely enhancing the repulsion effect at a lower point onthe face. The method wherein a weight member is provided is effective inits own way but limited in its usefulness under the recent tendency forclub heads to increase in size. That is, when a club head becomes largein size, addition of a weight member gives rise to a new problem thatthe mass of the head becomes heavy. The golf industry is a world wheretradition is valued originally.

[0011] Substantial changes in the configuration, weight, etc. of theclub head from those of the conventional one require users to changetheir golf swing and so forth. This may cause the swing rhythm to bedestroyed. Even if an epoch-making golf club is developed, it will takea long time for the new golf club to become established in actualpractice. Thus, various problems will occur if large-scale changes aremade to the configuration of golf clubs that have actually beenestablished. Therefore, it is ideal to develop a golf club improved infunction to satisfy golfers without substantial change in theconfiguration of the presently established golf clubs.

[0012] Accordingly, it is desired to develop a golf club capable ofenlarging the repulsion area, particularly, downward on the club headface, without making a large difference from the conventionalconfiguration and without requiring a special arrangement that limitsthe functions of the golf club, whereby the repulsion performance isimproved even at a lower point on the club head face as well as in theconventional sweet area, and thus the ball traveling distance can beincreased stably even under headwind conditions.

SUMMARY OF THE INVENTION

[0013] The present invention was made in view of the above-describedtechnical background. Accordingly, the present invention attains thefollowing objects.

[0014] An object of the present invention is to provide a golf clubimproved to increase repulsive force at a lower point on the club headface so that the ball can be hit farther without a decrease in balltraveling distance even if it is struck at a point below theconventional sweet area.

[0015] Another object of the present invention is to provide a golf clubimproved in ball hitting performance in comparison to the conventionalgolf clubs, despite having the same basic configuration as theconventional one, simply by modifying a part of the club head sole,without a change from the conventional structure in terms of theconfiguration as seen from the player upon addressing.

[0016] Still another object of the present invention is to provide agolf club capable of being produced at reduced costs.

[0017] To attain the above-described objects, the present inventionprovides the following golf clubs.

[0018] According to a first aspect thereof, the present inventionprovides a golf club having a metallic hollow golf club head. The golfclub includes a face member disposed at the front of the club head andhaving a hitting surface for hitting a golf ball. The golf club furtherincludes a head body member constituting the remaining part of the clubhead. The head body member has a sole forming the bottom of the clubhead, a crown forming the top of the club head, a toe forming theforepart of the club head, a heel forming the rear part of the clubhead, a back positioned opposite the face member to form the back partof the club head, and a hosel to which a club shaft is connected. Adeformable area that is elastically deformable in response to hitting ofthe golf ball on the hitting surface is provided at the joint betweenthe lower end of the face member and the sole.

[0019] A golf club according to a second aspect of the present inventionis a golf club of the first aspect, wherein the deformable area includesa lower end portion of the face member that is bent at an angle not lessthan 90 degrees to form a bent portion, and the sole is joined to thebent portion. The sole is convexly projected toward the top of the clubhead in a section taken along a vertical plane containing a lineperpendicular to the hitting surface.

[0020] A golf club according to a third aspect of the present inventionis a golf club of the first aspect, wherein the deformable area includesa lower end portion of the face member that is bent at an angle not lessthan 90 degrees to form a bent portion, and the sole is jointed to thebent portion. The sole is convexly projected away from the top of theclub head in a section taken along a vertical plane containing a lineperpendicular to the hitting surface.

[0021] A golf club according to a fourth aspect of the present inventionis a golf club of the first aspect, wherein the deformable area includesa lower end portion of the face member that is bent at an angle not lessthan 90 degrees to form a bent portion, and the sole is joined to thebent portion. The sole is provided with at least one hole.

[0022] A golf club according to a fifth aspect of the present inventionis a golf club of the first aspect, wherein the deformable area includesa lower end portion of the face member that is bent at an angle not lessthan 90 degrees to form a bent portion, and the sole is joined to thebent portion. The sole has a part thereof replaced with a thin plate.

[0023] A golf club according to a sixth aspect of the present inventionis a golf club of the first aspect, wherein the deformable area includesa lower end portion of the face member that is bent at an angle not lessthan 90 degrees to form a bent portion, and the sole is joined to thebent portion. The sole is divided into two portions at a part thereof.The two portions are displaceable relative to each other.

[0024] A golf club according to a seventh aspect of the presentinvention is a golf club of the second or third aspect, wherein the solein the deformable area has a smaller plate thickness than that of thebent portion.

[0025] A golf club according to an eighth aspect of the presentinvention is a golf club of the second aspect, wherein a part of thesole in the deformable area forms an arch-shaped groove.

[0026] A golf club according to a ninth aspect of the present inventionis a golf club of the second aspect, wherein a portion of the sole thatis joined to the bent portion in the deformable area forms a groovehaving a surface approximately parallel to the hitting surface.

[0027] A golf club according to a tenth aspect of the present inventionis a golf club of the seventh aspect, wherein the deformable area has agentle bend G formed by intersection of a line S₁ tangent to the surfaceof the face member with a line S₂ tangent to the bent portion of theface member. The bend G has an angle α not less than 90 degrees. Thedeformable area further has a gentle bend H formed by intersection ofthe tangent line S₂ with a line S₃ tangent to the surface of the sole.The bend H has an angle α₁ not less than 90 degrees.

[0028] A golf club according to an eleventh aspect of the presentinvention is a golf club of the tenth aspect, wherein the deformablearea has at least one arch-shaped groove provided in a surface of thesole near the bend H. A gentle bend J is formed by intersection of aline S₄ tangent to the groove with the tangent line S₂. The bend J hasan angle α₂ not less than 90 degrees. Further, a gentle bend K is formedby intersection of a line S₅ tangent to the groove with the tangent lineS₃. The bend K has an angle α₃ not less than 90 degrees. The bends G, Jand K form a continuous gently curved line.

[0029] A golf club according to a twelfth aspect of the presentinvention is a golf club of the tenth or eleventh aspect, wherein theangle α of the bend G is not less than 90 degrees and not more than 135degrees, preferably not less than 90 degrees and not more than 120degrees.

[0030] The above and other objects, features and advantages of thepresent invention will become more apparent from the followingdescription of the preferred embodiments thereof, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031]FIG. 1 is an external view showing the appearance of a golf club.

[0032]FIG. 2 is a plan view of a driver club head according to thepresent invention.

[0033]FIG. 3 is a front view of the driver club head according to thepresent invention.

[0034]FIG. 4 is a side view of the driver club head according to thepresent invention, which shows a first embodiment of the presentinvention.

[0035]FIG. 5 is a side view of a conventional driver club head.

[0036]FIG. 6 is a sectional view taken along the line X-X in FIG. 3.

[0037]FIG. 7 is a sectional view showing the details of the structureshown in FIG. 6.

[0038]FIG. 8 is an explanatory view illustrating a state where a golfball has been struck on the face of the club head.

[0039]FIG. 9 is a sectional view showing a third embodiment of thepresent invention.

[0040]FIG. 10 is a sectional view showing a fourth embodiment of thepresent invention.

[0041]FIG. 11 is a sectional view showing a fifth embodiment of thepresent invention.

[0042]FIG. 12 is a sectional view showing a sixth embodiment of thepresent invention.

[0043]FIG. 13 is a sectional view showing a seventh embodiment of thepresent invention.

[0044]FIG. 14 is a sectional view showing an eighth embodiment of thepresent invention, in which the club head has a groove with arectangular sectional configuration.

[0045]FIG. 15 is a sectional view showing a ninth embodiment, in whichthe club head has a groove with a stepped sectional configuration.

[0046]FIG. 16 is a sectional view showing a modification in which a partof the sole of the club head is made of a thin plate to lower therigidity of the sole.

[0047]FIG. 17 is a sectional view showing a modification in which thesole of the club head is divided into two portions to lower the rigidityof the sole.

[0048]FIG. 18 is a sectional view showing a modification in which thesole of the club head is provided with at least one hole to lower therigidity of the sole 3.

[0049]FIG. 19 is a diagram showing the distribution of coefficients ofrestitution in the club head according to the first embodiment.

[0050]FIG. 20 is a diagram showing the distribution of coefficients ofrestitution in a conventional club head.

[0051]FIG. 21 is an explanatory view showing a measurement comparison asto ball traveling distance between the first embodiment and theconventional golf club.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] Embodiments of the present invention will be described below indetail with reference to the accompanying drawings.

[0053]FIG. 1 is an external view showing the general structure of a golfclub according to the present invention. Although the present inventionis directed to a metallic hollow golf club head, the followingdescription of embodiments will be made of an example in which thepresent invention is applied to a driver club head. A driver club head(hereinafter referred to simply as “head”) 1 is supported on a shaft A.FIGS. 2 to 4 show an embodiment of the head 1 as used in a metallic golfclub. It should be noted that the drawings other than FIG. 1 show onlythe head part. That is, illustration of the shaft A and other members isomitted therein.

[0054]FIG. 2 is a plan view. FIG. 3 is a front view, and FIG. 4 is aside view. As shown in the figures, the head 1 comprises a crown 2corresponding to the top of the head 1, a sole 3 corresponding to thebottom of the head 1, a face 4 with which a golf ball is struck, a toe 5corresponding to the forepart of the head 1, a heel 6 corresponding tothe rear part of the head 1, a back 12 positioned opposite the face 4 toform the back part of the head 1, and a hosel 7, which is a member forsupporting the head 1 on the shaft A.

[0055] In the manufacture of the head 1, each part comprises either asingle unitized member or a plurality of equally divided members thatare joined together to form one component part. Each component part issubjected to press working before being joined together into anintegrated structure by welding or the like. For example, the head 1comprises five component parts, i.e. a face 4, a sole 3, a crown 2, ahosel 7, and a weight. Each part is produced as follows. A platematerial is blanked into a predetermined shape. The blank is formedunder heating by hot pressing. The heating process is performed, forexample, at 400° C. for the face 4, and at 900° C. for the sole 3, thecrown 2 and other portions of the head body.

[0056] After being pressed, each component part is deburred (trimmed)and joined together by TIG arc welding to produce a driver club head 1.In this embodiment, the constituent material of the head 1 is a titaniumalloy. The component parts are joined together as follows. Theconstituent members related to the face 4 and those related to the sole3 are butt-joined to each other. Thereafter, the hosel-related membersare joined thereto, and the pressed crown-related members are joined byTIG arc welding. In this way, the component parts are integrated into adriver club head 1. After the welding process, the driver club head issubjected to grinding process and age hardening (5 hours at 515° C.),followed by painting process. Thus, the driver club head is completed.

[0057] The face 4 has a slightly curved surface and is formed from aplate-shaped material. In the face 4, a sweet area 9 in the vicinity ofthe center 8 of gravity has the maximum coefficient of restitution.Usually, an effective way of sending a golf ball a long distance is tohit the ball at the sweet area 9. Therefore, the coefficient ofrestitution is set high in this portion of the face 4. It is well knownthat as the coefficient of restitution is increased, the ball travelingdistance increases. The coefficient of restitution is an importantfactor determining the performance of golf clubs. For the coefficient ofrestitution, a criterion of measurement has been defined by the UnitedStates Golf Association (USGA). The coefficient of restitution isobtained from the following equation:

V _(out) /V _(in) =eM−m/M+m

[0058] In the above equation, m represents the average mass of balls fortesting, M represents the mass of the head, V_(out) represents the speedof a testing ball after impact, and V_(in) represents the speed of thetesting ball before impact. Accordingly, V_(out)/V_(in) shows the speedratio. Further, e represents the coefficient of restitution. Accordingto the definition, golf balls for testing should be Pinnacle Gold (tradename) golf balls, and testing balls that have previously been numberedand measured for initial velocity should be used. The average weightshould be 45.4 g.

[0059] It is defined that the testing balls should be stored in a roomat 23±1.0° C., and the impact speed should be 48.8 m/s. In addition, aball launching apparatus, a trajectory screen and other testingequipment have been specified in detail. Regarding a testing methodalso, rules have been made in detail. For example, mapping should beperformed. A reference value of the coefficient of restitution ise=0.822. Whether each particular head is conformable or not is judged bycomparing the actual impact speed ratio with the reference speed ratioon the basis of the measured mass according to the above-describeddefinition.

[0060] Meanwhile, the coefficient of restitution can be calculatedinversely from the above-described equation, provided that the otherconditions are determined. In other words, the coefficient ofrestitution is calculated for various values of the mass of the headthat may be changed, for example, by varying the thickness of the face4. In this way, it is possible to judge optimal numerical value setting.As will be clear from the above-described equation, the fact that thespeed of a golf ball after impact is high means that the coefficient ofrestitution is high.

[0061] The present inventor conducted exhaustive studies by performingtesting according to the above-described rules and attained the presentinvention in which the conventional sweet area is extended downward andthus widened.

[0062] Embodiments of the present invention will be described below indetail. FIG. 5 is a side view of a conventional driver club head, whichcorresponds to a side view of the first embodiment of the presentinvention shown in FIG. 4. As will be understood from comparison withFIG. 5, the present invention has an improvement made on the sole 3. Asshown in FIG. 4, a portion of the sole 3 closer to the face 4 isprovided with a projection 10 and a groove 11 that extend in a directionconnecting the toe 5 and the heel 6. The projection 10 projects awayfrom the crown 2, and the groove 11 is recessed toward the crown 2. Theprojection 10 comprises a first projection 10 a and a second projection10 b facing each other across the groove 11. The first projection 10 ais located closer to the face 4. The second projection 10 b is formed asa gentle projection extending toward the heel 6, which is the rear partof the head 1.

[0063] As shown in FIG. 4, the projection 10 and the groove 11 have agently curved configuration as a whole. The face-side projection 10 amakes the sole 3 form an obtuse angle α to the face 4 (see FIG. 6) in asection taken along a vertical plane (plane containing a straight linein a direction shown by a thread suspending an object) containing a lineperpendicular to the surface of the face 4. The purpose of providing arecessed and projected area on the sole 3 is to impart an elastic effectto the sole 3. The recessed and projected area as an elasticallydeformable area B is a constituent part featuring this embodiment. FIG.6 is a sectional view taken along the line X-X in FIG. 3, schematicallyshowing the first embodiment.

[0064] The head 1 is a component formed by press working, as has beenstated above. Accordingly, a portion of the head 1 corresponding to theexternal line of the head structure shown in FIG. 6 is defined bypressed members formed of a titanium alloy. The interior C is a hollowspace. In FIG. 6, line D shows the position of the sole of theconventional club head. In contrast thereto, this embodiment has astructure in which the sole 3 partly projects and has the deformablearea B at a position closer to the face 4, as shown in FIG. 6. Theprojecting height E of the deformable area B is of the order of 6 mm inthis embodiment. When impact force F is applied to the surface of theface 4 in the direction of the arrow shown in FIG. 6, the head itself iselastically deformed complicatedly. In this embodiment, the elasticdeformation is made concentrated toward the sole 3 as much as possibleby providing the recessed and projected deformable area B on the sole 3.

[0065] As a result, the sole 3 has a considerable elastic effect even ifthe face 4 is left unchanged from the conventional configuration andeven if compared to a conventional structure in which the thickness ofthe lower portion of the face 4 is reduced to increase repulsive force,for example. Thus, it is possible to avoid the problem that the rigidityof the head is undesirably weakened by excessively reducing thethickness of the face 4 with the intention of increasing repulsiveforce. The deformable area B is not necessarily limited to theconfiguration shown in this embodiment. The deformable area B may haveany configuration that produces an elastic effect. However, it ispreferable for the deformable area B to have a recessed and/or projectedconfiguration.

[0066]FIG. 6 is a schematic view of the X-X section of FIG. 3, whereasFIG. 7 is a detailed view of the X-X section. Next, the structure of thedeformable area B will be described in detail with reference to FIG. 7.As has been stated above, the face 4 is bent at a lower portion thereoftoward the sole 3 to form a bent portion 4 a. The curving part betweenthe face 4 and the bent portion 4 a constitutes a first bend G.

[0067] The first bend G means a part formed by intersection of a line S₁tangent to the face 4 approximately at the center thereof with a line S₂tangent to the bent portion 4 a approximately at the center thereof. Thebend G is defined by a gently curved surface contiguous to the tangentlines S₁ and S₂ at the point of intersection thereof. The angle α of thebend G is not less than 90 degrees and not more than 135 degrees.Preferably, the angle α is not less than 90 degrees and not more than120 degrees. This has been confirmed on the basis of measured data. Theangle α is measured by using a protractor. The surface of the face 4 isrounded approximately uniformly. Therefore, the measurement is carriedout in such a manner that when the protractor is applied to the surfaceof the face 4, that is, when a tangent is drawn to the face surface, thegap between the straight line and the curved line is approximately thesame at the left and right sides or at the upper and lower sides. Thebent portion 4 a as bent constitutes a part of the sole 3.

[0068] An end portion of the sole 3 is joined to the distal end of thebent portion 4 a by welding. The plate thickness t₂ of the sole 3 issmaller than the plate thickness t₁ of the face 4. In the embodimentillustrated in the figures, an arch-shaped groove I (11) is provided inthe sole 3. The groove I is defined by a gently curved line extendingimmediately from the end of the sole 3. The end of the arch-shapedgroove I forms a continuous gently curved line and constitutes a thirdbend J in combination with the bent portion 4 a. The third bend J isformed as a gentle bend by intersection of the tangent line S₂ to thebent portion 4 a approximately at the center-thereof with a line S₄tangent to approximately one rising portion of the groove I. The angleα₂ of the bend J is an obtuse angle not less than 90 degrees.

[0069] Further, the groove I constitutes a gently curved fourth bend Kin combination with a portion of the sole 3 closer to the back 12. Thefourth bend K is formed as a gentle bend by intersection of a line S₅tangent to approximately the other rising portion of the groove I with aline S₃ tangent to the sole 3. The angle α₃ of the bend K is an obtuseangle not less than 90 degrees. Although the illustrated example hasonly one arch-shaped groove I, a plurality of arch-shaped grooves may beprovided. Each of the bends G, J and K, including the groove I,constitutes a part of the deformable area B. With the above-describedstructure of the deformable area B, the face-side portion of the head 1is kept highly rigid as in the conventional club head, and the rigidityof the sole-side portion of the head 1 is made lower than that of theface-side portion of the head 1.

[0070] It should be noted that the sectional configuration shown in FIG.7 is provided with a single recess (as seen from the outside of the sole3). In other words, the sectional configuration shown in FIG. 7 is asfollows. Assuming that the angle (α) of clockwise rotation from thetangent line S₁ to the tangent line S₂ is a plus angle and the angle (α)of counterclockwise rotation is a minus angle, the rotation angle (α)changes between plus and minus sequentially: the angle (α) is plus inrotation from the tangent line S₁ to the tangent line S₂, plus inrotation from the tangent line S₂ to the tangent line S₄, minus inrotation from the tangent line S₄ to the tangent line S₅, and plus inrotation from the tangent line S₅ to the tangent line S₃. The fact thatthere are sequential plus rotations and one minus rotation from thetangent line S₁ to the tangent line S₃, that is, there is one rotationangle change between plus and minus, means that the sole 3 is formedwith one recess. If there are two rotation angle changes between plusand minus, it means that the sole 3 is formed with two recesses. In theexample shown in FIG. 7, the angle change between plus and minus iswithin 90 degrees. This means that the recess is a concave groove havinga gentle curvature.

[0071] If there is no angle change from plus to minus, the sole 3 has norecess. In other words, the head structure may have, roughly speaking, asectional configuration along a linear contour defined by the tangentlines S₂ and S₃ intersecting each other, in which the sole 3 has asecond bend H formed from a projection, as shown in FIG. 7. The secondbend H is formed as a gentle bend by intersection of the line S₂ tangentto the bent portion 4 a with the line S₃ tangent to the surface of thesole 3 approximately at the center thereof. The angle α₁ of the secondbend H is an obtuse angle not less than 90 degrees.

[0072] The crown 2 has the same structure as in the conventional clubhead. The face-side portion of the crown 2 looks unchanged from theconventional structure as seen from the player upon addressing. Becausethe sole-side portion of the head 1 is made lower in rigidity than theface-side portion of the head 1, the lower portion of the face 4 iseasily deflectable upon hitting a golf ball. With the gently curvedstructure, the shock is lessened, and the likelihood of the head 1 beingcracked at impact is eliminated. In addition, the spring effect isenhanced. Consequently, the conventional sweet area extends toward thesole 3. That is, the sweet area widens downward. Thus, the repulsioneffect is enhanced.

[0073] If a golf ball is struck at a lower point on the face 4 (at aposition below approximately 60% of the height of the face 4 from thesole 3), the lower portion of the surface of the face 4 is deflected bya spring effect produced by deflection of the sole 3 through the gentlycurved portion and the groove I, thereby enhancing the repulsion effect.As a result, the golf club according to this embodiment enables theconventional sweet area to extend downward on the surface of the face 4and hence allows the sweet area to be widened. Accordingly, even if theplayer strikes a golf ball at a lower point on the face 4, there will beno decrease in ball traveling distance as occurs with the conventionalgolf clubs. Thus, the golf club according to this embodiment enables theplayer to stably get better distance. Further, because it has a widenedsweet area, the head 1 of this embodiment is capable of increasing themaximum coefficient of restitution.

[0074]FIG. 8 is an explanatory view schematically showing a state wherea ball has been struck on the hitting surface of the face 4. This is thestate F shown in FIG. 6. The theoretical contents of the above-describedstructure of the embodiment will be explained below in detail withreference to FIG. 8. When a ball 23 is struck on the face 4, the face 4is deformed toward the back 12 as shown by the chain double-dashed linein the figure. The ball 23 is also deformed. If the amount ofdeformation of the ball 23 is reduced, the hysteresis loss due todeformation of the ball 23 when it returns to the previous sphericalshape by its own elasticity is reduced, and thus the impact energy lossof the ball 23 is minimized. If the amount of deformation of the face 4is increased, the amount of deformation of the ball 23 can be reducedrelatively. Consequently, it is possible to increase the coefficient ofrestitution and to hit the ball 23 a longer distance.

[0075] When the ball 23 is struck on the face 4, the sole 3 is alsodeformed downward in association with the deformation of the face 4. Inthe conventional club head, the angle formed between the face 4 and thesole 3 is an acute angle, as shown in FIG. 5. Therefore, the face 4 andthe sole 3 are not sufficiently deformable. In this embodiment, however,the angle between the face 4 and the sole 3 is set not less than 90degrees, as shown by G in FIG. 7. As a result, the face 4, particularlya region below the center of the surface of the face 4, is lower inrigidity than in the conventional club head and hence easily elasticallydeformable upon hitting the ball 23. Thus, the lower portion of the face4 is elastically deformed to a considerable extent in comparison to theconventional club head by a synergistic effect of the face 4 and thesole 3. For this reason, when the ball 23 is struck on a lower portionof the hitting surface of the face 4, the ball 23 is sent a longerdistance effectively without lowering the coefficient of restitution incomparison to the conventional club head.

[0076]FIG. 9 shows a second embodiment of the present invention. In thiscase, a portion of the sole 3 closer to the face 4 is formed with only aprojection 13 projecting flat in comparison to the conventional clubhead on the assumption that the bend between the face 4 and the sole 3is formed at an obtuse angle α in a section taken along a vertical planecontaining a line perpendicular to the surface of the face 4. Incomparison to the arrangement of the foregoing embodiment, the club headaccording to this embodiment has no groove but a flat projection 13between the back 12 and the face 4. When an impact is applied to theface 4, the projection 13 is elastically deformed to increase thecoefficient of restitution of the club head.

[0077]FIG. 10 shows a third embodiment of the present invention, inwhich the whole sole 3 is curvedly projected outward as a projection 14over from the face 4 to the back 12.

[0078]FIG. 11 shows a fourth embodiment of the present invention, inwhich the whole sole 3 is curvedly projected inward as a recess 15 overfrom the face 4 to the back 12.

[0079]FIG. 12 shows a fifth embodiment of the present invention, inwhich a part of the bent portion 4 a closer to the joint with the sole 3is bent approximately parallel to the face 4 to form a bent portion 16having a turn-back surface. The sole 3 extending from the bent portion16 to the back 12 is approximately flat and in a straight-line form inthe sectional view of FIG. 12. When an impact is applied to the face 4,the bent portion 16 is deformed to a considerable extent.

[0080]FIG. 13 shows a sixth embodiment of the present invention. In thiscase, a portion of the sole 3 closer to the face 4 is formed with aplurality of recesses and projections on the assumption that the bendbetween the face 4 and the sole 3 is formed at an obtuse angle α in asection taken along a vertical plane containing a line perpendicular tothe surface of the face 4. As shown in the figure, three projections 17and two grooves 18 are provided. The repulsion effect is the same as theabove. However, the recessed and projected configuration is somewhatsmaller in size than in the above-described example owing to therestriction on the space.

[0081]FIGS. 14 and 15 show seventh and eighth embodiments, respectively,of the present invention, in which the groove I (11) is modified. InFIG. 14, the club head has a groove 19 with a rectangular sectionalconfiguration. In FIG. 15, the club head has a groove 20 with a steppedsectional configuration. Both the seventh and eighth embodiments providethe same advantageous effects as the above.

[0082]FIG. 16 shows a modification in which the club head is arranged tolower the rigidity of the sole 3. That is, a part of the sole 3 is madeof a thin plate 21 to lower the rigidity of the sole 3.

[0083]FIG. 17 shows a modification in which the club head is arranged tolower the rigidity of the sole 3. The sole 3 is divided into twoportions 3 a and 3 b so that when an impact is applied to the face 4,the divided portions 3 a and 3 b are slidable relative to each other.

[0084]FIG. 18 shows a modification in which the club head is arranged tolower the rigidity of the sole 3. A part of the sole 3 closer to theface 4 is provided with at least one hole 22 to lower the rigidity ofthe sole 3.

[0085] Although various embodiments have been described above, thepresent invention is not necessarily limited to the describedembodiments. The deformable area B preferably has the above-describedrecessed and/or projected configuration. However, the deformable area Bmay have a gentle V-shaped configuration or a bellows-likeconfiguration. The deformable area B may have any configuration,provided that it enhances the elastic effect and lowers the rigidity ofthe sole 3.

EXAMPLES

[0086] The following is a description of examples carried out to examinethe improvement in performance with regard to the above-described clubhead structures. FIG. 19 shows the results of an experiment carried outon the golf club according to the first embodiment. FIG. 19 shows adistribution of coefficients of restitution measured when a golf ballwas struck on the face 4. Based on the experimental results, points ofthe same coefficient of restitution were plotted as contour lines. FIG.20 shows the results of an experiment carried out on a conventional golfclub under the same conditions as in the case of FIG. 19. Theexperiments were performed under the following conditions: Facematerial: cold rolled material of Ti-15V-3Cr-3Sn-3Al plate thickness:2.9 mm Sole material: Ti-15V-3Cr-3Sn-3Al plate thickness: 1.15 mm Crownmaterial: Ti-15V-3Cr-3Sn-3Al plate thickness: 1.0 mm Volume: about 300cc mass: about 196 g.

[0087] It will be clear from comparison of FIG. 19 with FIG. 20 thathigh values of the coefficient of restitution are distributed closer tothe sole side in FIG. 19. This means that even if a golf ball is struckat a point on the face surface closer to the sole, the ball can be hit afarther distance than with the conventional golf club.

[0088]FIG. 21 shows measurements of ball traveling distance obtained bya hitting test using a golf ball hitting robot to compare the embodimentof the present invention with a conventional golf club. FIG. 21 shows ameasurement comparison at a head speed of 40 m/s. The height H of thepoint of measurement is the distance from the leading edge, as shown inFIG. 21. In FIG. 21, Example represents the first embodiment of thepresent invention, and Comparative Example represents a conventionalgolf club. The test was performed by using a golf ball hitting robot.Example and Comparative Example were carried out under the same hittingconditions. The hitting conditions are as shown in FIG. 21.

[0089] The specifications of the clubs used in the test are as follows:Club length: 44.5 inches Balance: D2 Loft angle β: 10.5 degrees Lieangle γ: 56.5 degrees Shaft FLEX: R

[0090] In comparison of the measurements of ball travelling distance, ata point of measurement at a height H of 18 mm, for example, the balltravelling distance of Example is 204 yards, whereas that of ComparativeExample is 199 yards. It will be clear from the difference in the balltravelling distance that the structure of the present invention isadvantageously effective.

[0091] As has been detailed above, the golf club according to thepresent invention is arranged such that the sole of the club head has anelastic effect. Accordingly, repulsive force obtained at a lower pointon the face is increased. Therefore, even if a golf ball is struck at apoint below the conventional sweet area, the ball can be hit a longdistance without a decrease in ball traveling distance.

[0092] Further, the basic configuration of the club head is leftunchanged from that of the conventional golf clubs, but only a part ofthe sole of the club head is modified. Therefore, the externalappearance of the club head looks unchanged from the conventionalstructure as seen from the player upon addressing. Nevertheless, thegolf club according to the present invention exhibits improvedball-hitting performance in comparison to the conventional golf clubs.Further, the procedure for imparting the elastic effect to the sole ofthe club head can be carried out by press working in the same process asthat for the conventional golf clubs except that the press die needs tobe changed. Therefore, there is no increase in production costs, and thegolf club according to the present invention can be produced by the samemanufacturing process as that for the conventional golf clubs despitethe improvement in performance.

[0093] It should be noted that the present invention is not necessarilylimited to the foregoing embodiments but can be modified in a variety ofways without departing from the gist of the present invention.

What is claimed is:
 1. A golf club having a metallic hollow golf clubhead, said golf club comprising: a face member disposed at a front ofsaid club head and having a hitting surface for hitting a golf ball; anda head body member constituting a remaining part of said club head, saidhead body member including: a sole forming a bottom of said club head; acrown forming a top of said club head; a toe forming a forepart of saidclub head; a heel forming a rear part of said club head; a backpositioned opposite said face member to form a back part of said clubhead; and a hosel to which a club shaft is connected; wherein adeformable area that is elastically deformable in response to hitting ofthe golf ball on said hitting surface is provided at a joint between alower end of said face member and said sole.
 2. A golf club according toclaim 1, wherein said deformable area includes a lower end portion ofsaid face member that is bent at an angle not less than 90 degrees toform a bent portion, said sole being joined to said bent portion, saidsole being convexly projected toward the top of said club head in asection taken along a vertical plane containing a line perpendicular tosaid hitting surface.
 3. A golf club according to claim 1, wherein saiddeformable area includes a lower end portion of said face member that isbent at an angle not less than 90 degrees to form a bent portion, saidsole being jointed to said bent portion, said sole being convexlyprojected away from the top of said club head in a section taken along avertical plane containing a line perpendicular to said hitting surface.4. A golf club according to claim 1, wherein said deformable areaincludes a lower end portion of said face member that is bent at anangle not less than 90 degrees to form a bent portion, said sole beingjoined to said bent portion, said sole being provided with at least onehole.
 5. A golf club according to claim 1, wherein said deformable areaincludes a lower end portion of said face member that is bent at anangle not less than 90 degrees to form a bent portion, said sole beingjoined to said bent portion, said sole having a part thereof replacedwith a thin plate.
 6. A golf club according to claim 1, wherein saiddeformable area includes a lower end portion of said face member that isbent at an angle not less than 90 degrees to form a bent portion, saidsole being joined to said bent portion, said sole being divided into twoportions at a part thereof, said two portions being displaceablerelative to each other.
 7. A golf club according to claim 2 or 3,wherein said sole in said deformable area has a smaller plate thicknessthan that of said bent portion.
 8. A golf club according to claim 2,wherein a part of said sole in said deformable area forms an arch-shapedgroove.
 9. A golf club according to claim 2, wherein a portion of saidsole that is joined to said bent portion in said deformable area forms agroove having a surface approximately parallel to said hitting surface.10. A golf club according to claim 7, wherein said deformable area has agentle bend G formed by intersection of a line S₁ tangent to a surfaceof said face member with a line S₂ tangent to said bent portion, saidbend G having an angle α not less than 90 degrees, and a gentle bend Hformed by intersection of said tangent line S₂ with a line S₃ tangent toa surface of said sole, said bend H having an angle α₁ not less than 90degrees.
 11. A golf club according to claim 10, wherein said deformablearea has at least one arch-shaped groove provided in a surface of saidsole near said bend H, and wherein a gentle bend J is formed byintersection of a line S₄ tangent to said groove with said tangent lineS₂, said bend J having an angle α₂ not less than 90 degrees, and agentle bend K is formed by intersection of a line S₅ tangent to saidgroove with said tangent line S₃₁ said bend K having an angle α₃ notless than 90 degrees, wherein said bend G, said bend J and said bend Kform a continuous gently curved line.
 12. A golf club according to claim10 or 11, wherein the angle α of said bend G is not less than 90 degreesand not more than 135 degrees, preferably not less than 90 degrees andnot more than 120 degrees.